1. Field of Invention
The present invention relates to a method for detecting failure of a paper detector in a roll paper printer constructed so that opening the cover to the roll paper compartment opens the paper transportation path, and to a roll paper printer having control for detecting failure of a paper detector.
2. Description of Related Art
Roll paper printers constructed so that opening the cover to the roll paper compartment also opens the paper transportation path from the roll paper compartment passed the printing position of the print head to the paper exit so that the roll paper can be easily loaded and replaced are known from the literature. See, for example, JP-A-2002-264414.
This type of roll paper printer may have a paper detector for detecting if a web of the recording paper that is delivered (pulled) from the paper roll is present in the transportation path, and a cover detector for detecting if the cover to the roll paper compartment is opened and closed and may issue an appropriate warning if there is no paper present or if the cover is open.
However, if the paper detector fails and indicates that the printing paper is present even though the paper is not present in the paper transportation path, problems such as soiling of the platen and other parts will occur. For example, if the print head is an inkjet head ink droplets will be discharged directly onto the surface of the platen, and the platen surface will be soiled with ink.
Paper presence can be detected optically (using photosensors), magnetically (using magnetic sensors), or mechanically (using microswitches), and detection errors (detector failure) can occur due to aging or due to an initial defect in the paper detector. If an optical paper detector including a photointerrupter and a detection lever is used, detection errors can result due to faulty installation of the detection lever, a fault in the photointerrupter circuit, and operating errors caused by aging of the detector lever or circuit board, for example.
Conventional roll paper printers cannot, however, detect failure of such paper detectors. As a result, the paper detector may indicate that paper is present even though there is no paper, the printing operation executes with no paper present, and the platen becomes dirty or is damaged. In addition to the faulty paper detector, it may even become necessary to replace the platen.